Tamper-resistant brake actuator

ABSTRACT

The present invention provides a tamper-resistant fluid-operated brake actuator having a power spring housed within a head or cap which is attached to a flange case having one or more diaphragms or pistons responsive to changes of fluid pressure within the brake actuator chambers. In one embodiment, the head is attached to the flange case by a substantially continuous curvilinear annular metal retaining member which must be inelastically deformed or destroyed in order to remove the head from the flange case, thus rendering tampering more difficult. In another embodiment, the annular metal retaining member of the present invention is integral with the actuator head and which is metal-spun or the like onto the flange case.

This is a continuation of application Ser. No. 07/910,464 filed Jul. 8,1992, now U.S. Pat. No. 5,311,809.

The present invention relates generally to braking systems and, morespecifically, to fluid-operated brake actuators such as air brakeactuators.

BACKGROUND OF THE INVENTION

Fluid-operated braking systems such as air brake systems have long beenused to control the movement of motor vehicles in a safe and effectivemanner. In particular, air brakes are commonly used on commercialvehicles such as trucks which typically have large gross vehicleweights. The considerable inertial mass of these heavy-duty vehicles incombination with the high speeds at which they travel requires a brakingsystem which responds rapidly with substantial braking power. One systemcomponent which is instrumental in the operation of air brake systems isthe brake actuator. The brake actuator provides the force necessary whenbraking a vehicle. The assignee of the present invention produces anumber of high-quality commercial air brake actuators, many of whichactuate the normal service brakes as well as parking/emergency brakes.These brake actuators, also known as spring brakes, typically have anetwork of air chambers defined by one or more diaphragms or pistons anda plurality of springs which operate to provide the appropriate brakingaction in response to directives by the vehicle driver. In the event anair braking system loses pressure, the brake actuator automaticallyengages the vehicle brakes.

Brake actuators of this type, with or without a service brake section,have a powerful coil spring seated within a housing or head portion ofthe actuator. When compressed, the power spring exerts a biasing forcein an axial direction relative to the housing. The power spring has ahigh spring constant such that, once compressed, it has a substantialamount of potential energy. When released, the stored energy of thespring is converted into kinetic energy to be used in the brakingoperation. However, premature removal of the actuator head, that is,removal of the head while the power spring is compressed, may cause thisenergy to be released in an undesirable manner. For example, theactuator cap or head assembly is typically attached to the flange caseusing a single or multiple section ring clamp, the clamp being securedin position by one or more retaining bolts. In the field, theinjudicious removal of these retaining bolts may release the ring clampcausing the head or cap to detach from the case flange. Once released,the immense energy of the spring is transmitted to the actuator headwhich is propelled away from the flange case with considerable force.Hence, the air pressure which retains the power spring in its compressedstate must be dissipated prior to the removal of the clamp, and thepower spring must be "caged" within the head. Moreover, these prior artclamp rings can be difficult to position when assembling the actuator.

Typically, instructions are attached to the brake actuators to informthose attempting inspection or repair of the presence of the powerspring and of the consequences which may result from tampering with thehead retaining ring clamp when the power spring is in the compressedstate, evidencing recognition by the art of the tampering problem.However, it would still be desirable to provide a device for attachingthe actuator head to the flange case in a manner which would preventremoval in the field.

Restraining and clamping devices have been proposed by others foraddressing the improvident detachment of a brake actuator head from theflange case. In U.S. Pat. No. 4,565,120, a device for restraining theseparation of brake actuator housings is disclosed which consists of asheet metal body having a notch which receives the housing flanges. Thenotch is large enough to permit partial separation of the housingflanges upon release of the flange clamp band. A number of clampingbands are also known such as those disclosed in U.S. Pat. Nos.3,106,757, CLAMP STRUCTURE FOR METAL BANDS, 3,295,176, HOSE CLAMPS,4,583,773, RELEASABLE TUBULAR CLAMPS FOR THE CONNECTION OF CYLINDRICALOR PROFILED TUBES, 4,451,955, CRIMP-TYPE CLAMP, 4,430,775, MUFFLERSHIELD BANDING STRAP, 3,602,954, ANNULAR HOSE CLIP, 2,541,205, and4,109,350, CLAMP BAND. For a variety of reasons, none of these latterclamping devices, however, are appropriate for providing atamper-resistant brake actuator, nor is any such use disclosed orsuggested by these references which are considered to be non-analogousart with respect to brake actuators. Thus, to meet this need, thepresent invention provides a reliable tamper-resistant fluid-operatedbrake actuator.

SUMMARY OF THE INVENTION

In accordance with the present invention, a tamper-resistantfluid-operated brake actuator is provided which includes a head or capwhich encloses a power spring that is intermittently compressed by anair-actuated diaphragm and piston which form a moveable wall. The brakeactuator head is attached to the flange case by an annular metalretaining member having either a substantially continuous or axiallyslotted curvilinear shape. The annular metal retaining member ispartially formed in place on the flange of the flange case, attachingthe head such that the annular metal retaining member must be cut orotherwise inelastically deformed for the head to be removed from theflange case. In one aspect, the annular metal retaining member of theinventive tamper-resistant brake actuator comprises a metal-spun orcrimped rim or ring integral with the actuator head. Suitable formingmethods in addition to metal spinning and the like are also provided. Inthis embodiment, the annular metal retaining member is spun or crimpedonto the flange case providing dependable tamper-resistant attachment ofthe head to the flange case. The head or cap having the integral annularmetal retaining member may be suitably spun or crimped onto the flangecase using a lathe or equivalent device and an appropriate tool usingconventional metal spinning or coining techniques. Also, a press-typedevice and appropriate fixturing for metal crimping techniques may beused. Forming methods other than metal spinning or crimping may besuitable.

In another embodiment of the present invention, the tamper-resistantbrake actuator of the present invention includes an annular metalretaining member which is a unitary element that comprises a clampingring which is fitted onto the abutting rim and flange of the head andflange case. After the clamping ring is placed in its initial positionon the flange and rim, it is deformed beyond its elastic limit at atensioning portion to form a tamper-resistant attachment of the head tothe flange case. In this embodiment, the annular metal retaining memberpreferably includes a recessed or cut-out section which provides a flexregion which facilitates installation. Chamfered ring surfaces whichmate with the rim flange are also preferably provided to permit easyattachment of the deformable retaining member.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional side elevational view of thetamper-resistant brake actuator of the present invention.

FIG. 2 is a top view of the brake actuator shown in FIG. 1 illustratinga clamping band having two retaining bolts for the service brakesection.

FIG. 3 is a cross-sectional side elevational view of the brake actuatordepicted in FIG. 1 in an intermediate stage of fabrication.

FIG. 4 is a side elevational view of the brake actuator of the presentinvention in another embodiment with a portion of the actuator brokenaway, the broken-away portion being shown in cross-section.

FIG. 5 is a top view of one embodiment of the deformable retainingmember of the present invention.

FIG. 6 is a side elevational view of the deformable retaining member ofFIG. 5 shown in cross-section.

FIG. 7 illustrates the tensioning of the deformable retaining membershown in FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1 of the drawings, in one embodiment of thepresent invention, brake actuator 20 is shown generally, illustratedhere as a double-diaphragm air brake actuator having an external tubebreather system 21. Brake actuator 20 includes service chamber assembly22 and spring chamber assembly 24. Flange case and push rod subassembly26 is shown having flange case 28 and push rod 30. Connected by push rodplate retaining screw 33 to one end of push rod 30 is spring side pushrod plate 32. Spring guide 34 is provided to hold return spring 36 inposition. To the other end of push rod 30, service side push rod plate38 is attached by push rod plate retaining screw 40. During operation,push rod 30 moves axially in relation to flange case 28 on the bearingsurfaces of push rod guide bushings 42 in contact with push rod caseseal 44. Service chamber assembly 22 similarly includes push rod 46 towhich service side piston 48 is attached. Non-pressure chamber 50 isdefined by service housing 52 which encloses return spring 54.Conventional mounting bolts 56 and yoke assembly 58 are also shown.Other brake actuator assemblies may be suitable in the presentinvention.

As will be understood by those skilled in the art, fluid or "air brakes"of this nature are controlled by the movement of one or more flexiblediaphragms and rigid piston plates which combine to form a moveable wallwhen actuated by air pressure differentials created in the variouschambers of brake actuator 20. Hence, brake actuator 20 is equipped withdiaphragm 60 having an expanded outside diameter portion or simplyexpanded portion 62 in the nature of an integral O-ring or the like.Diaphragm 60 forms a hermetic or air-tight seal by the compression ofexpanded portion 62 at the interface of service housing 52 and flangecase 28. Hence, diaphragm 60 is formed of a resilient material such asrubber, neoprene, fabric-center reinforced neoprene or the like. Inorder to obtain this compression of expanded portion 62 and to attachservice housing 52 to flange case 28, clamping ring 64 is positionedover annular flange portion 66 of housing 52 and annular flange portion68 of flange case 28.

Clamp ring 64 is shown more fully in FIG. 2 having two semicircularportions 70 and 72 each having tabs or ears 74 through which clampretaining bolts 76 are inserted to tighten clamp 64 in position bytightening retaining nuts 77 on bolts 76. This is, clamp 64 secureshousing 52 to flange case 28 and compresses expanded portion 62 ofdiaphragm 60 forming an air-tight seal. This conventional constructionof clamp 64 is suitable for the attachment of housing 52 to flange ease28 since return spring 54 is not a power spring. One piece, single-boltclamps of this type are also known.

Returning to FIG. 1 of the drawings, spring side diaphragm 78 is shownhaving expanded portion 80 which is again in the nature of an integralO-ring or the like. Portion 80 is seated in annular groove 82 of annularflange 84 of flange case 28. Thus, spring side push rod plate 32 isadjacent one side of diaphragm 78 while spring side piston 86 isadjacent the other side of diaphragm 78. Brake actuator 20 is shown inFIG. 1 in the normal driving mode. In this mode and in the normalservice brake mode, spring side piston 86 compresses heavy-duty powerspring 88 within cap or head 90 by virtue of the air pressure exerted ondiaphragm 78 through inlet 91. Diaphragm 78 and spring side piston 86form a first moveable wall held in the illustrated position by airpressure in this mode of operation. A head assembly 92 is thus definedby head 90 and diaphragm 78. Head 90 is provided with aperture 94 shownclosed with dust cover or plug 96 secured to head 90 by dust plug screw98 and retained on head 90 with an interference fitting, annular linedflange. Aperture 94 provides access to piston 86 using a release bolt(not shown in FIG. 1).

In the normal service brake mode, air is injected through inlet 99causing diaphragm 60 and service side piston 48 to move downwardly. Itwill be understood that diaphragm 60 and service side piston 48 form asecond moveable wall which is air-pressure responsive. The downwardmovement of this second moveable wall causes push rod 46 to thrust outfrom service housing 52 to set the vehicle brakes.

Hence, when chamber 100 is sufficiently pressurized with air which issupplied through inlet 91, the moveable wall formed by diaphragm 78 andthus spring side piston 86 are held in the position shown in FIG. 1 sothat power spring 88 is, as stated, substantially compressed within headassembly 92. In this state, power spring 88 has a considerable amount ofstored or potential energy. When chamber 100 is depressurized, diaphragm78 no longer holds spring side piston 86 which in response to thedepressurization moves axially with relation to push rod 30. In turn,the movement of push rod 30 causes push rod 46 to thrust out fromservice housing 52. It is this movement of push rod 46 which actuates orsets the vehicle brakes. When the movement of push rod 46 is caused bythe expansion of power spring 88, brake actuator 20 is in the parking oremergency brake mode. In this mode, springs 36 and 54 are compressed. Itwill therefore be understood that the spring constant of power spring 88is much greater than that of springs 36 and 54 in combination. Asdiaphragm 78 moves in response to the depressurization of chamber 100and the movement of spring side piston 86, air must enter head assembly92. This is achieved through vents 102 in head 90 via external tubebreather system 21 which reduces the uptake of atmospheric debris andthe like.

Hence, it is necessary that power spring 88 be compressed between piston86 and head 90 during normal driving and normal service brake mode. Inthese modes, power spring 88 exerts substantial force on head 90 in thedirection away from flange case 28. Although devices similar to clampingring 70 shown in FIG. 2 have in the past been used to connect or clamphead 90 to flange case 28 at flanges 84, as discussed earlier,improvident removal of such a clamp ring, which can be accomplishedsimply by removing retaining nut 77, will cause head 90 to separate fromflange case 28 with considerable force. Improvident removal of head 90is avoided by the present invention by providing an annular metalretaining member 104 which, in this embodiment, is an integral portionof head 90.

Still referring to FIG. 1 of the drawings, deformable retaining member104 is shown in position on flange portion 84 of flange case 28compressing expanded portion 80 of diaphragm 78 to form an hermetic orair-tight seal. Hence, head 90 cannot be removed from flange case 28except by bending, prying, cutting or otherwise deforming or destroyingretaining member 104 to remove it from flange 84. That is, flange 84fits within a groove or channel defined by and coextensive with saidretaining member 104 and is securely assembled by spinning or bendingretaining member 104 over flange 84. It will be understood thatretaining member 104 and, as stated, flange 84 are annular orring-shaped, which may be a solid or interrupted section, such as anaxially slotted configuration which facilitates crimping, extendingaround the circumference or perimeter of brake actuator 20. Thus, theopportunity for the removal created by retaining bolt-type clamps isavoided. Not only will field removal be unlikely due to the increaseddifficulty of removing head 90, the prospect of reattaching head 90 toflange case 28 without specialized tools, provides further deterrence totampering.

Although other methods of forming retaining member 104 in place onflange 84 may be suitable, it is preferred that the attachment be madeby metal spinning, crimping, coining, or over-center forming techniqueswhich will be familiar to those skilled in the art.

Referring now to FIG. 3 of the drawings, brake actuator 20 is seen withretaining member 104 shown in an intermediate stage of construction.Head 90 has been placed in position on flange case 28. Note that thebrake actuator 20 is shown in FIG. 3 having power spring 88 in thecompressed mode, caged by release bolt 108. With head 90 in positionhaving retaining member 104 projecting over or overlying flange 84,retaining member 104 is deformed beyond its elastic limit using tool 106during metal spinning or forming to fasten retaining member 104 aroundflange 84. An alternate method would use a press to crimp a slottedretaining member around flange 84. The metal spinning operation may besuitably carried out using a lathe or equivalent device in the customarymanner. Although steel is the metal of choice for forming head 90 andretaining member 104 due to its easy machineability, other metals may besuitable. Head 90 is thus securely attached to flange case 28 by way ofspun-on retaining member 104 or a crimped on retaining member in atamper-resistant manner.

In another embodiment of the present invention and referring now to FIG.4 of the drawings brake actuator 107 is shown generally, again of thedouble diaphragm type. Like elements are designated using the samereference numerals as in the embodiment shown in FIGS. 1 through 3.Also, it is to be understood that while the present invention isdescribed in connection with a specific type of brake actuator and hasbeen illustrated with reference to a double diaphragm brake actuator,other fluid brake actuators may be made in accordance with the presentinvention such as piston type brake actuators, without regard to thetype of brakes, cam, disc or wedge, actuated by the brake actuator andwith or without external tube breather systems. The present invention isadaptable to virtually any brake actuator wherein a head which houses aspring is joined to a flange case or the like and all of these devicesare intended to come within the scope of the present invention.

Detachable release bolt 108 is shown in FIG. 4 having been inserted intoslot 110 of piston 86. Release bolt 108 is used to manually release thevehicle brakes when it is necessary to move the vehicle in the absenceair pressure or to reline the brakes. Note that release bolt 108 hasbeen inserted into position but release nut 109 has not yet been rotatedto draw piston 86 toward spring guide 89. Ports 91 and 99 through whichthe brake actuator chambers are pressurized and depressurized are alsoshown. Having a different configuration than head 90 of FIGS. 1 and 3,cap or head 116 is shown, again having an exhaust port 102 withassociated external tube breather system 21. In this embodiment, head116 is provided with a radially extending annular lip or rim 118. Rim118 extends completely around the perimeter of head 116. Flange 84 andflange case 28 have the same construction as shown in FIGS. 1 and 3,including annular groove or recess 82 in which expanded portion 80 ofdiaphragm 78 resides. However, annular metal retaining member 120 isshown comprising a unitary structure separate from head 116. Again,annular metal retaining member 120 provides tamper-resistant closure orattachment of head 116 to flanges case 28. Retaining member 120 in thisembodiment is in the nature of a circular channel clamp which receivesrim 118 and flange 84 thereby causing the compression of expandedportion 80 of diaphragm 78.

Retaining member 120 will be better understood with reference to FIG. 5of the drawings which shows retaining member 120 detached from itsposition on brake actuator 20. In this embodiment, retaining member 120comprises a ring of metal such as steel or the like and includestensioning or compression portion 122 which is formed by joining ends124 and 126 of body 128 of retaining member 120. Any number of means maybe used to join ends 124 and 126 as long as a strong connection isformed as by spot welding or the like. With reference now to FIG. 4,retaining member 120 is placed in position such that it receivesabutting rim 118 and flange 84 of brake actuator and groove or channel130, channel 130 being shown best in FIG. 6, which is a cross-section ofring body 128. Also, as shown in FIG. 6, chamfered or beveled surfaces132 are provided to facilitate the installation of retaining member 120onto abutted rim 118 and flange 84. That is, chamfered surfaces 132 actas guides or the like so that retaining member 120 can be easilyinstalled onto rim 118 and flange 84. It is to be understood that theinner diameter of the ring or circle formed by body 128 is "over-sized"to facilitate the placement of retaining member 120 over the flange 84and rim 118. Once retaining member 120 is in its initial position,referring now to FIG. 7, tools 134 are used to crimp tensioning portion122 to tighten body 128 around rim 118 and flange 84 so that head 116 istightly attached to flange case 28. That is, sections 136 of tensioningportion 122 are deformed beyond their elastic limit using tools 134 sothat body 128 of retaining member 120 is drawn snugly around head 116and flange case 28 reducing the diameter of deformable retaining member120. Thus, once fastened into position, retaining member 120 can beremoved only by deforming body 128 or tensioning portion 122 beyondtheir elastic limit or otherwise destroying retaining member 120. It ispreferred that body 128 be provided with recess 138 shown in FIG. 5which is simply a reduced portion of body 128. Bend relief or recess 138provides a flex point by which body 128 can be slightly flexed tofacilitate installation around head rim 118 and flange case 28 and toprovide even compression during assembly.

While the preferred embodiment of the present invention has beendescribed so as to enable one skilled in the art to practice thetechniques of the present invention, the description of the preferredembodiments is intended to be exemplary and does not limit the scope ofthe invention in any manner.

What is claimed is:
 1. A clamp which is to be deformed to secure twohousing portions together comprising:an elongated member, beinggenerally cylindrical and centered about a central axis, said elongatedmember having a cross-section which defines a channel to hold twohousing parts together in a plane passing through said central axis,said elongated member cross-section including a back portion extendinggenerally parallel to said central axis of said elongated member and twolegs extending radially inwardly towards said central axis from saidback portion, said legs extending at an angle from said back portionsuch that an included angle between said back portion and said leg isless than or equal to 90°, and the two housing parts which are heldtogether by said elongated member including at least a first housingpart having a first portion extending generally radially outwardly froma central axis and a second portion extending from the first portion inan axial direction, the other of the housing parts, including only afirst portion extending radially outwardly, and abutting an end of thesecond portion of the first housing part such that said two legs on saidelongated member can be placed outwardly of the first portion of thefirst housing member and the first portion of the second housing memberwith said back portion of said elongated member extending along thesecond portion of the first housing member; said elongated member havingtwo separate ends which are deformable together to secure the twohousing portions within said channel; and wherein a recessed portion ispositioned at a location diametrically opposed from said ends and saidrecessed portion facilitating flexing of said elongated member.
 2. Aclaim as recited in claim 1, wherein said two ends have a first portionextending generally radially outwardly from said central axis, and thenextend perpendicular to said first portion, and then parallel to atangent to the other periphery of said elongated body, said firstportions being deformable.
 3. A clamp which is to be deformed to securetwo housing portions together comprising:an elongated member, beinggenerally cylindrical and centered about a central axis, said elongatedmember having a cross-section which defines a channel to hold twohousing parts together in a plane passing through said central axis;said elongated member having two separate ends which are deformabletogether to secure the two housing portions within said channel, saidelongated member of cross-section including a back portion extendinggenerally parallel to a central axis of said elongated member and twolegs extending radially inwardly toward said central axis; wherein saidtwo ends have a first portion extending generally radially outwardlyfrom said central axis, and then extend perpendicular to said firstportion, and then parallel to a tangent to the outer periphery of saidelongated body, said first portions being deformable; and wherein arecessed portion is positioned at a diametrically opposed location fromsaid ends, said recessed portion having a smaller cross-sectional shapethan the portion of said elongated member between said ends and saidrecessed portion, said recessed portion facilitating the placement ofsaid clamp on the two housing members.